As one kind of common engineering machinery, cranes mainly include rail-mounted cranes and non-rail-mounted mobile cranes. The mobile cranes include all-terrain cranes, wheel-mounted cranes, crawler cranes, etc. The mobile cranes have some advantages, for example, having good trafficability and flexibility, traveling fast, transferring quickly and starting to work immediately after arriving at the destination. Thus, the mobile cranes are used widely in engineering construction. However, compared with the rail-mounted cranes, the mobile cranes have smaller lifting capability due to the limitation of their own weight. In order to improve the stability of a mobile crane in working, a counterweight is generally mounted on the mobile crane.
The counterweight is a main structural member of the mobile crane, and the weight of the counterweight has a great influence on the stability and lifting capability of the crane. A small-tonnage mobile crane generally adopts the self-mounted counterweight structure, in which the counterweight is fixedly mounted on the body of the mobile crane, such that moves and works along with the mobile crane. For the small-tonnage mobile crane, since the lifting weight is relatively small, the required weight of the counterweight is relatively small; since the counterweight is fixedly mounted on the body of the crane and there is no need to dismount the counterweight, the small-tonnage mobile crane has a compact structure as a whole and moves flexibly.
The mobile crane is gradually developed to be large-tonnage, super large-tonnage, and thus weight and spatial size of the counterweight for the mobile crane is constantly increased, and the volume of components of the crane is becoming larger and larger. However, the provision of the counterweight is limited by the road standard and the carrying capability of a chassis of the crane. Thus, the counterweight can rationally be disposed merely in a limited space. Generally, the counterweight is provided as a movable component, that is, the mobile crane does not carry the counterweight while travelling and the counterweight is mounted to the body of the crane while working. A counterweight mounting and dismounting mechanism is used to mount the counterweight to the body of the crane and to dismount the counterweight from the body of the crane.
In the structure of a conventional counterweight mounting and dismounting mechanism, a left lifting oil cylinder and aright lifting oil cylinder are symmetrically provided at two sides of a turntable. Piston rods of the left lifting oil cylinder and the right lifting oil cylinder are both oriented upwardly, and a left movable pulley and a right movable pulley are provided at top ends of the piston rods respectively. A left fixed pulley and a right fixed pulley are symmetrically provided at two sides of the turntable. One end of a left wire rope, which is wound around a pulley block consisting of the left movable pulley and the left fixed pulley, is fixed to the turntable, and the other end thereof is provided with a left lifting hook. One end of a right wire rope, which is wound around a pulley block consisting of the right movable pulley and the right fixed pulley, is fixed to the turntable, and the other end thereof is provided with a right lifting hook. A left locking oil cylinder and a right locking oil cylinder are also provided at the two sides of the turntable.
The above counterweight mounting and dismounting mechanism includes the lifting oil cylinders, the locking oil cylinders, the lifting wire ropes and the pulley blocks. The method for mounting the counterweight includes the following steps that: after the mobile crane is in position and legs are set, such that the turntable is capable of rotating, the mobile crane lifts the desired counterweight by its own lifting device onto a counterweight pallet which is located in an appropriate position on the ground at one side of the frame of the crane, then, the turntable is rotated such that a tail portion of the turntable provided with the counterweight mounting and dismounting device is rotated to a position right above the counterweight, and then the left and right lifting hooks are hooked with the counterweight pallet and are fixed by pins; subsequently, the lifting oil cylinders are protruded upwardly to lift the counterweight pallet together with the counterweight, and the pin holes are ensured to be aligned by positioning with a wedge on the turntable and a positioning block on the counterweight pallet, the left locking oil cylinder and the right locking oil cylinder are operated to allow the pins to reach out and to insert into fixing holes provided in the counterweight pallet so as to fix the counterweight pallet; and the left lifting oil cylinder and the right lifting oil cylinder are retracted slightly to avoid the left lifting oil cylinder, the right lifting oil cylinder, the left wire rope and the right wire rope from bearing weight during a lifting operation. The method for dismounting the counterweight is performed in a reverse process of the method for mounting the counterweight.
In the counterweight mounting and dismounting mechanism with such a structure, the left lifting oil cylinder, the right lifting oil cylinder, the left locking oil cylinder and the right locking oil cylinder are all provided on the turntable of the mobile crane. The volume of components of the large-tonnage mobile crane and the super large-tonnage mobile crane are relatively large. In order to ensure that the overall size of the mobile crane does not exceed the roadway traveling standard, the arrangement of components is relatively compact and the space between components is very limited. Thus, if the left lifting oil cylinder, the right lifting oil cylinder, the left locking oil cylinder and the right locking oil cylinder are further provided on the turntable, the space on the turntable will be very small, which will affect the normal rotation of the turntable and affect the working performance of the mobile crane severely. In addition, since the left lifting oil cylinder, the right lifting oil cylinder, the left locking oil cylinder and the right locking oil cylinder all have relatively large weight, if the arrangement is not reasonable, the force condition of the turntable is not reasonable, which will substantially affect the stability of the mobile crane. Furthermore, since the left lifting oil cylinder, the right lifting oil cylinder, the left locking oil cylinder and the right locking oil cylinder all have relatively large size, which results in an increased size of the whole mobile crane, and thus the overall size of the mobile crane could exceed the roadway travelling standard.